Triple-Diode Input & Local Digital Temp Sensor w/Two-Wire

LM83

LM83 Triple-Diode Input and Local Digital Temperature Sensor with Two-Wire

Interface

Literature Number: SNIS111A

LM83Triple-Diode Input and Local Digital Temperature Sensorwith Two-Wire InterfaceGeneral DescriptionThe LM83 is a digital temperature sensor with a 2 wire serialinterface that senses the voltage and thus the temperature ofthree remote diodes using a Delta-Sigma analog-to-digitalconverter with a digital over-temperature detector. The LM83accurately senses its own temperature as well as the tem-perature of three external devices, such as Pentium II® Pro-cessors or diode connected 2N3904s. The temperature ofany ASIC can be detected using the LM83 as long as a dedi-cated diode (semiconductor junction) is available on the die.Using the SMBus interface a host can access the LM83’sregisters at any time. Activation of a T_CRIT_A output oc-curs when any temperature is greater than a programmablecomparator limit, T_CRIT. Activation of an INT output occurswhen any temperature is greater than its corresponding pro-grammable comparator HIGH limit.

The host can program as well as read back the state of theT_CRIT register and the four T_HIGH registers. Three statelogic inputs allow two pins (ADD0, ADD1) to select up to 9SMBus address locations for the LM83. The sensor powersup with default thresholds of 127˚C for T_CRIT and allT_HIGHs. The LM83 is pin for pin and register compatiblewith the LM84 as well as the Maxim MAX1617 and the Ana-log Devices ADM1021.

Featuresn Accurately senses die temperature of 3 remote ICs, or

diode junctions

n On-board local temperature sensingn SMBus and I2C compatible interface, supports

SMBus 1.1 TIMEOUTn Two interrupt outputs: INT and T_CRIT_An Register readback capabilityn 7 bit plus sign temperature data format, 1 ˚C resolutionn 2 address select pins allow connection of 9 LM83s on a

single bus

Key Specificationsj Supply Voltage 3.0V to 3.6V

j Supply Current 0.8mA (max)

j Local Temp Accuracy (includes quantization error)

0˚C to +85˚C ±3.0˚C (max)

j Remote Diode Temp Accuracy (includes quantizationerror)

+25˚C to +100˚C ±3˚C (max)

0˚C to +125˚C ±4˚C (max)

Applicationsn System Thermal Managementn Computersn Electronic Test Equipmentn Office Electronicsn HVAC

Simplified Block Diagram

SMBus™ is a trademark of the Intel Corporation.Pentium II® is a registered trademark of the Intel Corporation.I2C® is a registered trademark of the Philips Corporation.

DS101058-1

November 1999LM

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LocalDigitalTem

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Interface

© 2000 National Semiconductor Corporation DS101058 www.national.com

Connection Diagram Ordering Information

OrderNumber

NSPackageNumber

TransportMedia

LM83CIMQAMQA16A

(QSOP-16)95 Units in

Rail

LM83CIMQAXMQA16A

(QSOP-16)

2500 Units onTape andReel

Typical Application

Pin Description

Label Pin # Function Typical Connection

D1+, D2+, D3+ 1, 3, 5

Diode Current Source To Diode Anode. Connected to remote discretediode junction or to the diode junction on a remoteIC whose die temperature is being sensed. Whennot used they should be left floating.

VCC 2Positive Supply VoltageInput

DC Voltage from 3.0 V to 3.6 V

QSOP-16

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TOP VIEW

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Pin Description (Continued)

Label Pin # Function Typical Connection

D− 4Diode Return CurrentSink

To all Diode Junction Cathodes using a starconnection to pin. Must float when not used.

ADD0–ADD1 10, 6User-Set SMBus (I2C)Address Inputs

Ground (Low, “0”), VCC (High, “1”) or open(“TRI-LEVEL”)

GND 7, 8 Power Supply Ground Ground

NC 9, 13, 15

Manufacturing test pins. Left floating. PC board traces may be routedthrough the pads for these pins, although thecomponents that drive these traces should sharethe same supply as the LM83 so that the AbsoluteMaximum Rating, Voltage at Any Pin, is notviolated.

INT 11Interrupt Output,open-drain

Pull Up Resistor, Controller Interrupt or Alert Line

SMBData 12SMBus (I2C) SerialBi-Directional Data Line,open-drain output

From and to Controller, Pull-Up Resistor

SMBCLK 14 SMBus (I2C) Clock Input From Controller, Pull-Up Resistor

T_CRIT_A 16Critical TemperatureAlarm, open-drain output

Pull Up Resistor, Controller Interrupt Line orSystem Shutdown

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Absolute Maximum Ratings (Note 1)

Supply Voltage −0.3 V to 6.0 VVoltage at Any Pin −0.3 V to

(VCC + 0.3 V)D− Input Current ±1 mAInput Current at All Other Pins (Note2) 5 mAPackage Input Current (Note 2) 20 mASMBData, T_CRIT_A, INT OutputSink Current 10 mASMBCLK, SMBData, T_CRIT_A, INTOutput Voltage 6.0 VStorage Temperature −65˚C to +150˚CSoldering Information, Lead Temperature

QSOP Package (Note 3)Vapor Phase (60 seconds) 215˚CInfrared (15 seconds) 220˚C

ESD Susceptibility (Note 4)Human Body Model 2000 VMachine Model 200 V

Operating Ratings(Notes 1, 5)

Specified Temperature Range TMIN to TMAX

LM83 −40˚C to +125˚CSupply Voltage Range (VCC) +3.0V to +3.6V

Temperature-to-Digital Converter CharacteristicsUnless otherwise noted, these specifications apply for VCC=+3.0Vdc to 3.6Vdc. Boldface limits apply for T A = TJ = TMIN toTMAX; all other limits TA= TJ=+25˚C, unless otherwise noted.

Parameter Conditions Typical Limits Units

(Note 6) (Note 7) (Limit)

Temperature Error using LocalDiode ((Note 8))

TA = 0 ˚C to +85˚C,VCC=+3.3V

±1 ±3 ˚C (max)

TA = −40 ˚C to +125˚C,VCC=+3.3V

±4 ˚C (max)

Temperature Error using RemoteDiode ((Note 8))

TA = +60 ˚C to +100˚C,VCC=+3.3V

±3˚C (max)

TA = 25 ˚C to +100˚C,VCC=+3.3V

±3 ˚C (max)

TA = 0 ˚C to +125˚C,VCC=+3.3V

±4 ˚C (max)

Diode Channel to Channel Matching 0 ˚C

Resolution 8 Bits

1 ˚C

Conversion Time of AllTemperatures

(Note 10) 460 600 ms (max)

Quiescent Current (Note 9) SMBus (I2C) Inactive 0.500 0.80 mA (max)

D− Source Voltage 0.7 V

Diode Source Current (D+ − D−)=+ 0.65V; highlevel

125 µA (max)

60 µA (min)

Low level 15 µA (max)

5 µA (min)

T_CRIT_A and INT OutputSaturation Voltage

IOUT = 3.0 mA 0.4V (max)

Power-On Reset Threshold On VCC input, fallingedge

2.31.8

V (max)V (min)

Local and Remote T_CRIT andHIGH Default Temperature settings

(Note 11) +127 ˚C

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Logic Electrical CharacteristicsDIGITAL DC CHARACTERISTICSUnless otherwise noted, these specifications apply for VCC=+3.0 to 3.6 Vdc. Boldface limits apply for T A = TJ = TMIN toTMAX; all other limits TA= TJ=+25˚C, unless otherwise noted.

Symbol Parameter Conditions Typical Limits Units


SMBData, SMBCLK

VIN(1) Logical “1” Input Voltage 2.1 V (min)

VIN(0) Logical “0”Input Voltage 0.8 V (max)

VIN(HYST) SMBData and SMBCLK DigitalInput Hysteresis

300 mV

IIN(1) Logical “1” Input Current VIN = VCC 0.005 1.5 µA (max)

IIN(0) Logical “0” Input Current VIN = 0 V −0.005 1.5 µA (max)

ADD0, ADD1

VIN(1) Logical “1” Input Voltage VCC 1.5 V (min)

VIN(0) Logical “0”Input Voltage GND 0.6 V (max)

IIN(1) Logical “1” Input Current VIN = VCC 2 µA (max)

IIN(0) Logical “0” Input Current VIN = 0 V -2 µA (max)

ALL DIGITAL INPUTS

CIN Input Capacitance 20 pF

ALL DIGITAL OUTPUTS

IOH High Level Output Current VOH = VCC 100 µA (max)

VOL SMBus Low Level OutputVoltage

IOL = 3 mAIOL = 6 mA

0.40.6

V (max)

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Logic Electrical Characteristics (Continued)

SMBus DIGITAL SWITCHING CHARACTERISTICSUnless otherwise noted, these specifications apply for VCC=+3.0 Vdc to +3.6 Vdc, CL (load capacitance) on output lines = 80pF. Boldface limits apply for T A = TJ = TMIN to TMAX; all other limits TA = TJ = +25˚C, unless otherwise noted.The switching characteristics of the LM83 fully meet or exceed the published specifications of the SMBus or I2C bus. The fol-lowing parameters are the timing relationships between SMBCLK and SMBData signals related to the LM83. They are not theI2C or SMBus bus specifications.

Symbol Parameter Conditions Typical Limits Units


fSMB SMBus Clock Frequency 10010

kHz (max)kHz (min)

tLOW SMBus Clock Low Time 10 % to 10 % 1.325

µs (min)ms (max)

tLOWMEXT Cumulative Clock Low Extend Time 10 ms (max)

tHIGH SMBus Clock High Time 90 % to 90% 0.6 µs (min)

tR,SMB SMBus Rise Time 10% to 90% 1 µs (max)

tF,SMB SMBus Fall Time 90% to 10% 0.3 ns (max)

tOF Output Fall Time CL = 400 pF,IO = 3 mA

250 ns (max)

tTIMEOUT SMBData and SMBCLK Time Low forReset of Serial Interface (Note 12)

2540

ms (min)ms (max)

t1 SMBCLK (Clock) Period 10 µs (min)

t2,tSU;DAT

Data In Setup Time to SMBCLK High 100 ns (min)

t3,tHD;DAT

Data Out Stable after SMBCLK Low 300TBD

ns (min)ns (max)

t4,tHD;STA

SMBData Low Setup Time to SMBCLKLow

100 ns (min)

t5,tSU;STO

SMBData High Delay Time afterSMBCLK High (Stop Condition Setup)

100 ns (min)

t6,tSU;STA

SMBus Start-Condition Setup Time 0.6 µs (min)

tBUF SMBus Free Time 1.3 µs (min)

SMBus Communication

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Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operatingthe device beyond its rated operating conditions.

Note 2: When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > VCC), the current at that pin should be limited to 5 mA. The 20 mAmaximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four.

Parasitic components and or ESD protection circuitry are shown in the figure below for the LM83’s pins. The nominal breakdown voltage of the zener D3 is 6.5 V.Care should be taken not to forward bias the parasitic diode, D1, present on pins: D+, D−, ADD1 and ADD0. Doing so by more than 50 mV may corrupt a temperatureor voltage measurement.

Pin Name D1 D2 D3 D4 Pin Name D1 D2 D3 D4

T_CRIT_A & INT x

VCC x SMBData x x

D+ x x x NC (pins 9 & 15) x x x

D− x x x x SMBCLK x x

ADD0, ADD1 x x x NC (pin 13) x xNote: An x indicates that the diode exists.

Note 3: See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” or the section titled “Surface Mount” found in a current National Semicon-ductor Linear Data Book for other methods of soldering surface mount devices.

Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine model, 200 pF discharged directly into each pin.

Note 5: Thermal resistance of the QSOP-16 package is xyz˚C/W, junction-to-ambient when attached to a printed circuit board with 2 oz. foil as shown in Figure 3.

SMBus TIMEOUT

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See drawing DS10105807

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FIGURE 1. ESD Protection Input Structure

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Note 6: Typicals are at TA = 25˚C and represent most likely parametric norm.

Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

Note 8: The Temperature Error will vary less than ±1.0 ˚C for a variation in VCC of 3 V to 3.6 V from the nominal of 3.3 V.

Note 9: Quiescent current will not increase substantially with an active SMBus.

Note 10: This specification is provided only to indicate how often temperature data is updated. The LM83 can be read at any time without regard to conversion state(and will yield last conversion result).

Note 11: Default values set at power up.

Note 12: Holding the SMBData and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will cause the LM83 to reset SMBData and SMBCLK to the IDLEstate of an SMBus communication (SMBCLK and SMBData set High).

1.0 Functional DescriptionThe LM83 temperature sensor incorporates a band-gap typetemperature sensor using a Local or three Remote diodesand an 8-bit ADC (Delta-Sigma Analog-to-Digital Converter).The LM83 is compatible with the serial SMBus and I2C twowire interfaces. Digital comparators compare Local (LT) andRemote (D1RT, D2RT and D3RT) temperature readings touser-programmable setpoints (LHS, D1RHS, D2RHS,D3RHS and TCS). Activation of the INT output indicates thata comparison is greater than the limit preset in a HIGH reg-ister. The T_CRIT setpoint (TCS) interacts with all the tem-perature readings. Activation of the T_CRIT_A output indi-cates that any or all of the temperature readings haveexceed the T_CRIT setpoint.

1.1 CONVERSION SEQUENCE

The LM83 converts its own temperature as well as 3 remotediode temperatures in the following sequence:

1. Local Temperature (LT)

1. Remote Diode 2 (D2RT)



This round robin sequence takes approximately 480 ms tocomplete as each temperature is digitized in approximately120 ms.

1.2 INT OUTPUT and T_HIGH LIMITS

Each temperature reading (LT, D1RT, D2RT, and D3RT) isassociated with a T_HIGH setpoint register (LHS, D1RHS,D2RHS, D3RHS). At the end of a temperature reading a digi-tal comparison determines whether that reading has exceedits HIGH setpoint. If the temperature reading is greater thanthe HIGH setpoint, a bit is set in one of the Status Registers,to indicate which temperature reading, and the INT output isactivated.

Local and remote temperature diodes are sampled in se-quence by the A/D converter. The INT output and the Status

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FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)

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FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications

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1.0 Functional Description (Continued)

Register flags are updated at the completion of a conversion,which occurs approximately 60 ms after a temperature diodeis sampled. INT is deactivated when the Status Register,containing the set bit, is read and a temperature reading isless than or equal to it’s corresponding HIGH setpoint, asshown in Figure 4. Figure 5shows a simplified logic diagramfor the INT output and related circuitry.

The INT output can be disabled by setting the INT mask bit,D7, of the configuration register. INT can be programmed tobe active high or low by the state of the INT inversion bit, D1,in the configuration register. A “0” would program INT to beactive low. INT is an open-drain output.

1.3 T_CRIT_A OUTPUT and T_CRIT LIMIT

T_CRIT_A is activated when any temperature reading isgreater than the limit preset in the critical temperature set-point register (T_CRIT), as shown in Figure 6. The StatusRegisters can be read to determine which event caused thealarm. A bit in the Status Registers is set high to indicatewhich temperature reading exceeded the T_CRIT setpointtemperature and caused the alarm, see Section 2.3.

Local and remote temperature diodes are sampled in se-quence by the A/D converter. The T_CRIT_A output and theStatus Register flags are updated at the completion of a con-version. T_CRIT_A and the Status Register flags are resetonly after the Status Register is read and if a temperatureconversion is below the T_CRIT setpoint, as shown in Figure6. Figure 7 shows a simplified logic diagram of theT_CRIT_A and related circuitry.

Located in the Configuration Register are the mask bits foreach temperature reading, seeSection 2.5. When a mask bitis set, its corresponding status flag will not propagate to theT_CRIT_A output, but will still be set in the Status Registers.Setting all four mask bits or programming the T_CRIT set-point to 127˚C will disable the T_CRIT_A output.

1.4 POWER ON RESET DEFAULT STATES

LM83 always powers up to these known default states:

1. Command Register set to 00h

2. Local Temperature set to 0˚C

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* Note: Status Register Bits are reset by a read of Status Register wherebit is located.

FIGURE 4. INT Temperature Response Diagram withD2RHS and D3RHS set to 127˚C.

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FIGURE 5. INT output related circuitry logic diagram

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* Note: Status Register Bits are reset by a read of Status Register wherebit is located.

FIGURE 6. T_CRIT_A Temperature Response Diagramwith remote diode 1 and local temperature masked.

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FIGURE 7. T_CRIT_A output related circuitry logicdiagram

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3. Diode 1, Diode 2, and Diode 3 Remote Temperature setto 0˚C until the LM83 senses a diode present betweenthe D+ and D− input pins.

4. Status Registers 1 and 2 set to 00h.

5. Configuration Register set to 00h; INT enabled and allT_CRIT setpoints enabled to activate T_CRIT_A.

6. Local and all Remote T_CRIT set to 127˚C

1.5 SMBus INTERFACE

The LM83 operates as a slave on the SMBus, so theSMBCLK line is an input (no clock is generated by the LM83)and the SMBData line is bi-directional. According to SMBusspecifications, the LM83 has a 7-bit slave address. Bit 4 (A3)of the slave address is hard wired inside the LM83 to a 1.The remainder of the address bits are controlled by the stateof the address select pins ADD1 and ADD0, and are set byconnecting these pins to ground for a low, (0) , to VCC for ahigh, (1), or left floating (TRI-LEVEL).

Therefore, the complete slave address is:

A6 A5 A4 1 A2 A1 A0

MSB LSB

and is selected as follows:

Address Select Pin State LM83 SMBusSlave Address

ADD0 ADD1 A6:A0 binary

0 0 001 1000

0 TRI-LEVEL 001 1001

0 1 001 1010

TRI-LEVEL 0 010 1001

TRI-LEVEL TRI-LEVEL 010 1010

TRI-LEVEL 1 010 1011

1 0 100 1100

1 TRI-LEVEL 100 1101

1 1 100 1110

The LM83 latches the state of the address select pins duringthe first read or write on the SMBus. Changing the state ofthe address select pins after the first read or write to any de-vice on the SMBus will not change the slave address of theLM83.

1.6 TEMPERATURE DATA FORMAT

Temperature data can be read from the Local and RemoteTemperature, T_CRIT, and HIGH setpoint registers; and writ-ten to the T_CRIT and HIGH setpoint registers. Temperaturedata is represented by an 8-bit, two’s complement byte withan LSB (Least Significant Bit) equal to 1˚C:

Temperature Digital Output

Binary Hex

+125˚C 0111 1101 7Dh

+25˚C 0001 1001 19h

+1˚C 0000 0001 01h

0˚C 0000 0000 00h

−1˚C 1111 1111 FFh

−25˚C 1110 0111 E7h

−55˚C 1100 1001 C9h

1.7 OPEN-DRAIN OUTPUTS

The SMBData, INT and T_CRIT_A outputs are open-drainoutputs and do not have internal pull-ups. A “high” level willnot be observed on these pins until pull-up current is pro-vided from some external source, typically a pull-up resistor.Choice of resistor value depends on many system factorsbut, in general, the pull-up resistor should be as large aspossible. This will minimize any internal temperature readingerrors due to internal heating of the LM83. The maximum re-sistance of the pull up, based on LM83 specification for HighLevel Output Current, to provide a 2.1V high level, is 30kΩ.

1.8 DIODE FAULT DETECTION

Before each external conversion the LM83 goes through anexternal diode fault detection sequence. If a D+ input isshorted to VCC or floating then the temperature reading willbe +127 ˚C, and its OPEN bit in the Status Register will beset. If the T_CRIT setpoint is set to less than +127 ˚C thenthe D+ inputs RTCRIT bit in the Status Register will be setwhich will activate the T_CRIT_A output, if enabled. If a D+is shorted to GND or D−, its temperature reading will be 0 ˚Cand its OPEN bit in the Status Register will not be set.

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1.9 COMMUNICATING with the LM83

There are 19 data registers in the LM83, selected by theCommand Register. At power-up the Command Register isset to “00”, the location for the Read Local Temperature Reg-ister. The Command Register latches the last location it wasset to. Reading the Status Register resets T_CRIT_A andINT, so long as a temperature comparison does not signal afault (see Sections 1.2 and 1.3). All other registers are pre-defined as read only or write only. Read and write registerswith the same function contain mirrored data.

A Write to the LM83 will always include the address byte andthe command byte. A write to any register requires one databyte.

Reading the LM83 can take place either of two ways:

1. If the location latched in the Command Register is cor-rect (most of the time it is expected that the CommandRegister will point to one of the Read Temperature Reg-

isters because that will be the data most frequently readfrom the LM83), then the read can simply consist of anaddress byte, followed by retrieving the data byte.

2. If the Command Register needs to be set, then an ad-dress byte, command byte, repeat start, and another ad-dress byte will accomplish a read.

The data byte has the most significant bit first. At the end ofa read, the LM83 can accept either Acknowledge or No Ac-knowledge from the Master (No Acknowledge is typicallyused as a signal for the slave that the Master has read itslast byte).

1.10 SERIAL INTERFACE ERROR RECOVERY

The LM83 SMBus lines will be reset to the SMBus idle stateif the SMBData or SMBCLK lines are held low for 40 ms ormore (tTIMEOUT). The LM83 may or may not reset the state of

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the serial interface logic if either of the SMBData or SMBCLKlines are held low between 25 ms and 40 ms. TIMEOUT al-lows a clean recovery in cases where the master may be re-set while the LM83 is transmitting a low bit thus preventingpossible bus lock up.

Whenever the LM83 sees the start condition its serial inter-face will reset to the beginning of the communication, thusthe LM83 will expect to see an address byte next. This sim-plifies recovery when the master is reset while the LM83 istransmitting a high.

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2.0 LM83 REGISTERS

2.1 COMMAND REGISTER

Selects which registers will be read from or written to. Data for this register should be transmitted during the Command Byte ofthe SMBus write communication.

P7 P6 P5 P4 P3 P2 P1 P0

0 Command Select

P0-P7: Command Select

Command Se-lect Address

Power On Default State Register Name Register Function

<P7:P0> hex <D7:D0> binary <D7:D0> deci-mal

00h 0000 0000 0 RLT Read Local Temperature

01h 0000 0000 0 RD2RT Read D2 RemoteTemperature

02h 0000 0000 0 RSR1 Read Status Register 1

03h 0000 0000 0 RC Read Configuration

04h 0000 0000 0 Reserved

05h 0111 1111 127 RLHS Read Local HIGH Setpoint

06h Reserved

07h 0111 1111 127 RD2RHS Read D2 Remote HIGHSetpoint

08h Reserved

09h 0000 0000 WC Write Configuration

0Ah Reserved

0Bh 0111 1111 127 WD2LHS Write Local HIGH Setpoint

0Ch Reserved

0Dh 0111 1111 127 WD2RHS Write D2 Remote HIGHSetpoint

0Eh-2Fh Reserved for Future Use



32h-34h Reserved for Future Use

35h 0000 0000 0 RSR2 Read Status Register 2


38h 0111 1111 127 RD1RHS Read D1 Remote HIGHSetpoint

39h Reserved for Future Use

3Ah 0111 1111 127 RD3RHS Read D3 Remote HIGHSetpoint

3Bh-41h Reserved for Future Use

42h 0111 1111 127 RTCS Read T_CRIT Setpoint

43h-4Fh Reserved for Future Use

50h 0111 1111 127 WD1RHS Write D1 Remote HIGHSetpoint

51h Reserved for Future Use

52h 0111 1111 127 WD3RHS Write D3 Remote HIGHSetpoint


5Ah 0111 1111 127 WTCS Write T_CRIT Setpoint

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Command Se-lect Address

Power On Default State Register Name Register Function

<P7:P0> hex <D7:D0> binary <D7:D0> deci-mal

5Ch-6Fh andF0h-FDh

Reserved for Future Use

FEh 0000 0001 1 RMID Read Manufacturers ID

FFh RSR Read Stepping or DieRevision Code

2.2 LOCAL and D1, D2 and D3 REMOTE TEMPERATURE REGISTERS (LT, D1RT, D2RT, and D3RT)

(Read Only Address 00h, 01h, 30h and 31h):

D7 D6 D5 D4 D3 D2 D1 D0

MSB Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB

D7–D0: Temperature Data. One LSB = 1˚C. Two’s complement format.

2.3 STATUS REGISTERS 1 and 2

2.3.1 Status Register 1 (SR1) (Read Only Address 02h):

D7 D6 D5 D4 D3 D2 D1 D0

0 LHIGH 0 D2RHIGH 0 D2OPEN D2CRIT LCRIT

Power up default is with all bits “0” (zero).

D0: LCRIT: When set to a 1 indicates an Local Critical Temperature alarm.

D1: D2CRIT: When set to a 1 indicates a Remote Diode 2 Critical Temperature alarm.

D2: D2OPEN: When set to 1 indicates a Remote Diode 2 disconnect.

D4: D2RHIGH: When set to 1 indicates a Remote Diode 2 HIGH Temperature alarm.

D6: LHIGH: When set to 1 indicates a Local HIGH Temperature alarm.

D7, D5, and D3: These bits are always set to 0 and reserved for future use.

Status Register 22.3.2 Status Register 2 (SR2) (Read Only Address 35h):

D7 D6 D5 D4 D3 D2 D1 D0

D1RHIGH 0 D1OPEN D3RHIGH 0 D3OPEN D3CRIT D1CRIT


D0: D1CRIT, when set to 1 indicates a Remote Diode 1 Critical Temperature alarm.

D1: D3CRIT, when set to 1 indicates a Remote Diode 3 Critical Temperature alarm.

D2: D3OPEN, when set to 1 indicates a Remote Diode 3 disconnect.

D4: D3RHIGH, when set to 1 indicates a Remote Diode 3 HIGH Temperature alarm.

D5: D1OPEN, when set to 1 indicates a Remote Diode 1 disconnect.

D7: D1RHIGH, when set to 1 indicates a Remote Diode 1HIGH Temperature alarm.

D6, and D3: These bits are always set to 0 and reserved for future use.

2.4 MANUFACTURERS ID REGISTER

(Read Address FEh) Default value 01h.

2.5 CONFIGURATION REGISTER

(Read Address 03h/Write Address 09h):

D7 D6 D5 D4 D3 D2 D1 D0

INT mask 0 D1T_CRIT_A

mask

D2T_CRIT_A

mask

D3T_CRIT_A

mask

LocalT_CRIT_A

mask

INT Inversion 0


D7: INT mask: When set to 1 INT interrupts are masked.

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D5: T_CRIT mask for Diode 1, when set to 1 a Diode 1 temperature reading that exceeds T_CRIT setpoint will not activate theT_CRIT_A pin.



D2: T_CRIT mask for Local reading, when set to 1 a Local temperature reading that exceeds T_CRIT setpoint will not activatethe T_CRIT_A pin.

D1: INT active state inversion. When INT Inversion is set to a 1 the active state of the INT output will be a logical high. A low wouldthen select an active state of a logical low.

D6 and D0: These bits are always set to 0 and reserved for future use. A write of 1 will return a 0 when read.

2.6 LOCAL, DIODE 1, DIODE 2 and DIODE 3 HIGH SETPOINT REGISTERS (LHS, D1RHS, D2RHS and D3RHS)

(Read Address 05h, 07h, 38h, 3Ah /Write Address 0Bh, 0Dh,50h, 52h):

D7 D6 D5 D4 D3 D2 D1 D0


D7–D0: HIGH setpoint temperature data. Power up default is LHIGH = RD1HIGH=RD2HIGH=RD3HIGH = 127˚C.

2.7 T_CRIT REGISTER (TCS)

(Read Address 42h/Write Address 5Ah):

D7 D6 D5 D4 D3 D2 D1 D0


D7–D0: T_CRIT setpoint temperature data. Power up default is T_CRIT = 127˚C.

LM83

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3.0 SMBus Timing Diagrams

DS101058-10

(a) Serial Bus Write to the internal Command Register followed by a the Data Byte

DS101058-11

(b) Serial Bus Write to the internal Command Register

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(c) Serial Bus Read from a Register with the internal Command Register preset to desired value.

FIGURE 8. Serial Bus Timing Diagrams

LM83

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4.0 Application HintsThe LM83 can be applied easily in the same way as otherintegrated-circuit temperature sensors, and its remote diodesensing capability allows it to be used in new ways as well.It can be soldered to a printed circuit board, and because thepath of best thermal conductivity is between the die and thepins, its temperature will effectively be that of the printed cir-cuit board lands and traces soldered to the LM83’s pins. Thispresumes that the ambient air temperature is almost thesame as the surface temperature of the printed circuit board;if the air temperature is much higher or lower than the sur-face temperature, the actual temperature of the of the LM83die will be at an intermediate temperature between the sur-face and air temperatures. Again, the primary thermal con-duction path is through the leads, so the circuit board tem-perature will contribute to the die temperature much morestrongly than will the air temperature.

To measure temperature external to the LM83’s die, use aremote diode. This diode can be located on the die of a tar-get IC, allowing measurement of the IC’s temperature, inde-pendent of the LM83’s temperature. The LM83 has been op-timized to measure the remote diode of a Pentium IIprocessor as shown in Figure 9. A discrete diode can also beused to sense the temperature of external objects or ambientair. Remember that a discrete diode’s temperature will be af-fected, and often dominated, by the temperature of its leads.

Most silicon diodes do not lend themselves well to this appli-cation. It is recommended that a 2N3904 transistor baseemitter junction be used with the collector tied to the base.

A diode connected 2N3904 approximates the junction avail-able on a Pentium microprocessor for temperature measure-ment. Therefore, the LM83 can sense the temperature of thisdiode effectively.

3.1 ACCURACY EFFECTS OF DIODE NON-IDEALITYFACTOR

The technique used in today’s remote temperature sensorsis to measure the change in VBE at two different operatingpoints of a diode. For a bias current ratio of N:1, this differ-ence is given as:

where:

• η is the non-ideality factor of the process the diode ismanufactured on,

• q is the electron charge,

• k is the Boltzmann’s constant,

• N is the current ratio,

• T is the absolute temperature in ˚K.

The temperature sensor then measures ∆VBE and convertsto digital data. In this equation, k and q are well defined uni-versal constants, and N is a parameter controlled by the tem-perature sensor. The only other parameter is η, which de-pends on the diode that is used for measurement. Since∆VBE is proportional to both η and T, the variations in η can-not be distinguished from variations in temperature. Sincethe non-ideality factor is not controlled by the temperaturesensor, it will directly add to the inaccuracy of the sensor. Forthe Pentium II Intel specifies a ±1% variation in η from partto part. As an example, assume a temperature sensor hasan accuracy specification of ±3 ˚C at room temperature of 25˚C and the process used to manufacture the diode has anon-ideality variation of ±1%. The resulting accuracy of thetemperature sensor at room temperature will be:

TACC = ± 3˚C + (±1% of 298 ˚K) = ±6 ˚C.

The additional inaccuracy in the temperature measurementcaused by η, can be eliminated if each temperature sensor iscalibrated with the remote diode that it will be paired with.

3.2 PCB LAYOUT for MINIMIZING NOISE

In a noisy environment, such as a processor mother board,layout considerations are very critical. Noise induced ontraces running between the remote temperature diode sen-sor and the LM83 can cause temperature conversion errors.The following guidelines should be followed:

1. Place a 0.1 µF power supply bypass capacitor as closeas possible to the VCCpin and the recommended 2.2 nFcapacitor as close as possible to the D+ and D− pins.Make sure the traces to the 2.2nF capacitor arematched.

2. The recommended 2.2nF diode bypass capacitor actu-ally has a range of 200pF to 3.3nF. The average tem-perature accuracy will not degrade. Increasing the ca-pacitance will lower the corner frequency wheredifferential noise error affects the temperature readingthus producing a reading that is more stable. Con-versely, lowering the capacitance will increase the cor-ner frequency where differential noise error affects thetemperature reading thus producing a reading that isless stable.

3. Ideally, the LM83 should be placed within 10cm of theProcessor diode pins with the traces being as straight,short and identical as possible. Trace resistance of 1Ωcan cause as much as 1˚C of error.

4. Diode traces should be surrounded by a GND guard ringto either side, above and below if possible. This GNDguard should not be between the D+ and D− lines. In theevent that noise does couple to the diode lines it wouldbe ideal if it is coupled common mode. That is equally tothe D+ and D− lines.(See Figure 10)

5. Avoid routing diode traces in close proximity to powersupply switching or filtering inductors.

DS101058-15

Pentium or 3904 Temperature vs LM83 TemperatureReading

LM83

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4.0 Application Hints (Continued)

6. Avoid running diode traces close to or parallel to highspeed digital and bus lines. Diode traces should be keptat least 2cm. apart from the high speed digital traces.

7. If it is necessary to cross high speed digital traces, thediode traces and the high speed digital traces shouldcross at a 90 degree angle.

8. The ideal place to connect the LM83’s GND pin is asclose as possible to the Processors GND associatedwith the sense diode. For the Pentium II this would bepin A14.

9. Leakage current between D+ and GND should be keptto a minimum. One nano-ampere of leakage can causeas much as 1˚C of error in the diode temperature read-ing. Keeping the printed circuit board as clean as pos-sible will minimize leakage current.

Noise coupling into the digital lines greater than 300mVp-p(typical hysteresis), overshoot greater than 500mV aboveVCC, and undershoot less than 500mV below GND, may pre-vent successful SMBus communication with the LM83. SM-Bus no acknowledge is the most common symptom, causingunnecessary traffic on the bus. Although, the SMBus maxi-mum frequency of communication is rather low (100kHzmax) care still needs to be taken to ensure proper termina-tion within a system with multiple parts on the bus and longprinted circuit board traces. An R/C lowpass filter with a 3dbcorner frequency of about 40MHz has been included on theLM83’s SMBCLK input. Additional resistance can be addedin series with the SMBData and SMBCLK lines to furtherhelp filter noise and ringing. Minimize noise coupling bykeeping digital traces out of switching power supply areas aswell as ensuring that digital lines containing high speed datacommunications cross at right angles to the SMBData andSMBCLK lines.

4.0 Typical Applications

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FIGURE 10. Ideal Diode Trace Layout

DS101058-22

FIGURE 11. LM83 Demo Board Diode Layout

LM83

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4.0 Typical Applications (Continued)

DS101058-23

Any two or three D+ inputs can be connected in parallel to increase the number of High temperature setpoints for a particular temperature reading. If all threeD+ inputs are tied as shown here, D1+, D2+ and D3+ temperature readings will be identical, unless affected by PCB D+ trace resistance differences.

FIGURE 12. Connecting all Three LM83 Diode Inputs in Parallel will Increase the Number of HIGH Setpoints for aSingle Temperature Reading to Three.

LM83

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Physical Dimensions inches (millimeters) unless otherwise noted

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www.national.com

16-Lead QSOP PackageOrder Number LM83CIMQA or LM83CIMQAX

NS Package Number MQA16

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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Documents

Triple-Diode Input & Local Digital Temp Sensor w/Two-Wire